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United States Patent |
6,050,189
|
Junghans
,   et al.
|
April 18, 2000
|
Method for multicolor printing of nonabsorbent material, and a printing
press for printing in accordance with the method
Abstract
A method for multicolor printing of stock in web or plate form and having a
smooth, nonabsorbent surface, includes printing on the stock by the
indirect flexographic printing process; assigning each color to be printed
to a respective printing unit which includes an inking unit, a cylinder
for a flexographic printing form, a transfer cylinder and a
counterpressure cylinder; always drying the ink on the stock before
passing the stock to the next printing unit; and removing ink located in
indentations and on sides, respectively, of the printing surfaces of the
flexographic printing form; and a printing press for printing in
accordance with the method.
Inventors:
|
Junghans; Rudi (Wilhelmsfeld, DE);
Stadler; Peter (Heidelberg, DE);
Gotz; Emil (Geroldswil, CH)
|
Assignee:
|
Heidelberger Druckmaschinen AG (Heidelberg, DE)
|
Appl. No.:
|
023954 |
Filed:
|
February 17, 1998 |
Foreign Application Priority Data
| Feb 17, 1997[DE] | 197 06 154 |
| Nov 13, 1997[DE] | 197 50 259 |
Current U.S. Class: |
101/211; 101/174; 101/181; 101/349.1; 101/423 |
Intern'l Class: |
B41M 001/14; B41F 005/16; B41F 035/02; B41L 041/02 |
Field of Search: |
101/181,183,450.1,349.1,350.1,211,174,423,348
|
References Cited
U.S. Patent Documents
4397235 | Aug., 1983 | Fischer | 101/141.
|
4765243 | Aug., 1988 | Schiefer et al. | 101/451.
|
4939992 | Jul., 1990 | Bird.
| |
5651316 | Jul., 1997 | DeMoore et al. | 101/183.
|
5699740 | Dec., 1997 | Gelbart | 101/477.
|
Foreign Patent Documents |
1 251 688 | Mar., 1989 | CA.
| |
0 078 253 B1 | May., 1983 | EP.
| |
15 71 863 C3 | Jan., 1975 | DE.
| |
26 08 661 B2 | Aug., 1978 | DE.
| |
29 38 292 B2 | Jul., 1981 | DE.
| |
31 13 407 A1 | Nov., 1982 | DE.
| |
41 37 337 A1 | May., 1993 | DE.
| |
41 42 421 A1 | Jun., 1993 | DE.
| |
42 29 352 A1 | Apr., 1994 | DE.
| |
43 11 834 A1 | Oct., 1994 | DE.
| |
2 096 058 | Oct., 1982 | GB.
| |
Other References
Japanese Patent Abstract No. 4-185475 (A) (Yuasa), dated Jul. 2, 1992.
|
Primary Examiner: Asher; Kimberly R.
Attorney, Agent or Firm: Lerner; Herbert L., Greenberg; Laurence A., Stemer; Werner H.
Claims
We claim:
1. A method for multicolor printing of stock in web or plate form and
having a smooth, nonabsorbent surface, which comprises:
printing at least four colors on the stock by the indirect flexographic
printing process;
assigning each color to be printed to a respective printing unit which
includes an inking unit, a cylinder having a flexographic printing form
thereon, a transfer cylinder and a counterpressure cylinder;
always drying the ink on the stock before passing the stock to the next
printing unit;
removing ink located in indentations and on sides, respectively, of the
printing surfaces of the flexographic printing form using a roller
installed at a location where a dampening fluid application roller is
normally installed when using the respective printing unit for
lithographic printing; and
before each re-inking of the printing form, reapplying the removed ink as a
thin film.
2. The method according to claim 1, which includes printing with UV-curable
inks and, downstream of each printing unit, irradiating the printed stock
with UV light.
3. The method according to claim 1, wherein the printing form is a
metal-lined flexographic printing plate.
4. The method according to claim 1, wherein a conventional offset inking
unit applies the ink.
5. The method according to claim 1, which includes applying the ink with a
short inking unit to the flexographic printing form.
6. The method according to claim 1, which includes applying the ink to the
flexographic printing form with a screen roller cooperating with a chamber
doctor blade.
7. The method according to claim 1, which includes completely cleaning the
flexographic printing form a multiplicity of times during an ongoing
printing job.
8. The method according to claim 1, which comprises:
providing the roller with a soft surface; and
maintaining the flexographic printing form in continuous contact with the
soft surface of the roller during the printing process.
9. A method for multicolor printing of stock in web or plate form and
having a smooth, nonabsorbent surface, which comprises:
printing at least four colors on the stock by the indirect flexographic
printing process;
assigning each color to be printed to a respective printing unit which
includes an inking unit, a cylinder having a flexographic printing form
thereon, a transfer cylinder and a counterpressure cylinder;
always drying the ink on the stock before passing the stock to the next
printing unit; and
after every occurrence of a predetermined plurality of revolutions of the
cylinder having a flexographic printing form thereon, activating a washing
device for cleaning excess ink from the flexographic printing form
repeatedly during an ongoing printing job.
10. A method for multicolor printing of stock in web or plate form and
having a smooth, nonabsorbent surface, which comprises:
printing at least four colors on the stock by the indirect flexographic
printing process;
providing a sheet-fed offset press including at least four printing units;
providing each one of the printing units with an inking unit, a cylinder
having a flexographic printing form thereon, a transfer cylinder and a
counterpressure cylinder;
assigning each one of the colors to be printed to a respective one of the
printing units;
always drying the ink on the stock before passing the stock to the next
printing unit;
removing ink located in indentations and on sides, respectively, of the
printing surfaces of the flexographic printing form using a roller
installed at a location where a dampening fluid application roller is
normally installed when using the respective printing unit for
lithographic printing; and
before each re-inking of the printing form, reapplying the removed ink as a
thin film.
11. The method according to claim 10, which comprises printing with
UV-curable inks and, downstream of each printing unit, irradiating the
printed stock with UV light.
12. The method according to claim 10, wherein the printing form is a
metal-lined flexographic printing plate.
13. The method according to claim 10, wherein a conventional offset inking
unit applies the ink.
14. The method according to claim 10, which comprises applying the ink with
a short inking unit to the flexographic printing form.
15. The method according to claim 10, which comprises applying the ink to
the flexographic printing form with a screen roller cooperating with a
chamber doctor blade.
16. The method according to claim 10, which comprises completely cleaning
the flexographic printing form a multiplicity of times during an ongoing
printing job.
17. The method according to claim 10, which comprises:
providing the roller with a soft surface; and
maintaining the flexographic printing form in continuous contact with the
soft surface of the roller during the printing process.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for multicolor printing of stock or
printing materials which are in web or sheet or plate form and have a
smooth, nonabsorbent surface, such as plastic or metal plates, foils, or
plastic-coated papers, and so forth, and a printing press for printing in
accordance with the foregoing method.
In the conventional wet offset method, such materials can be printed only
with limitations. It would indeed be possible to print these materials by
the waterless offset process. However, the silicone surface of the dry
offset plates (Toray plates) is only conditionally resistant to the
required UV inks. The service life of the plates is shortened by
ultraviolet or UV inks. The vulnerability or sensitivity of the silicone
layer of waterless offset plates is contradictory to the required UV inks
and to the drying process or the process of anchoring the inks to the
surface of the plastic material.
In multicolor wet on wet printing, on the other hand, it is not possible to
achieve especially high quality with UV inks on plastic material.
The aforementioned materials are therefore generally printed at the present
time by flexographic printing, sometimes also with inks that are cured
with the aid of UV projectors immediately after the printing process. For
example, the book entitled "Technik des Flexodrucks" [Flexographic
Printing Technology] published in 1982 by DFTA-Flexodruck Fachgruppe e.V.
discloses the printing of such cylindrical containers as cans, tubes, and
so forth, in multiple colors with UV-curable inks by flexographic
printing. The machine or press described in this book on page 12.7 thereof
has a plurality of printing units having UV projectors disposed
therebetween, and are said also to be capable of printing by the indirect
letterpress method, i.e., the letterset process. Such machines are very
expensive, however, because they are built only by special order and are
not very worthy except for very large printing jobs and when they are in
use very frequently.
Moreover, limits are also set to the print quality, due to the use of
letterpress methods. One problem, for example, is that printing ink builds
up on the flexographic printing form and collects in the indentations on
the flexographic printing form, respectively, so that there are isolated
instances of ink being transferred to nonprinting regions of the
flexographic printing form.
German Patent 15 71 863 discloses a simple, direct letterpress method
wherein the residual film of ink remaining after the printing operation is
removed completely each time before the printing form is re-inked. The
residual ink film is removed from the printing form via ink removal
rollers and returned to the ink supply again. However, this German patent
makes no reference to the problems which arise in multicolor printing
especially on nonabsorbent surfaces.
Canadian Patent 1,251,688 describes a lithographic offset printing press
with a short inking unit and a dampening unit, wherein excess ink is
scraped from the wet offset plate with a doctor blade.
2. Summary of the Invention
It is accordingly an object of the invention to provide a method for
multicolor printing of nonabsorbent material by which stock or printing
materials in web or plate form with a nonabsorbent surface can be printed
in multiple colors simply and economically with high quality, and to
provide a printing press suitable for performing this method.
With the foregoing and other objects in view, there is provided, in
accordance with one aspect of the invention, a method for multicolor
printing of stock in web or plate form and having a smooth, nonabsorbent
surface, which comprises printing on the stock by the indirect
flexographic printing process, assigning each color to be printed to a
respective printing unit which includes an inking unit, a cylinder for a
flexographic printing form, a transfer cylinder and a counterpressure
cylinder, always drying the ink on the stock before passing the stock to
the next printing unit, and removing ink located in indentations and on
sides, respectively, of the printing surfaces of the flexographic printing
form.
In accordance with another mode, the method of the invention includes
printing with UV-curable inks and, downstream of each printing unit,
irradiating the printed stock with UV light.
In accordance with a further mode of the method of the invention, the
printing form is a metal-lined flexographic printing plate.
In accordance with an added mode, the method of the invention includes
applying the ink by a conventional offset inking unit.
In accordance with an additional mode, the method includes applying the ink
with a short inking unit to the flexographic printing plate.
In accordance with yet another mode, the method of the invention includes
applying the ink to the flexographic printing plate with a screen roller
cooperating with a chamber doctor blade.
In accordance with yet a further mode, the method of the invention includes
removing the ink in the indentations and on the sides, respectively, of
the printing surfaces of the flexographic printing form and reapplying
that ink as a thin film before each re-inking of the printing form.
In accordance with yet an additional mode, the method of the invention
includes completely cleaning the flexographic printing form a multiplicity
of times during an ongoing printing job.
In accordance with yet an added mode, the method of the invention includes
maintaining the flexographic printing form in continuous contact with a
soft roller during the printing process.
In accordance with another aspect of the invention, there is provided a
printing press for multicolor printing of stock in web or plate form and
having a smooth, nonabsorbent surface, comprising a plurality of
individual printing units, respectively, associated with a single color,
the printing units being arranged in rows and having at least one inking
unit, one cylinder for a flexographic printing form, one transfer cylinder
and one counterpressure cylinder, a plurality of drying devices for the
printing ink, respectively, assigned to one printing unit, and a plurality
of devices assigned to the flexographic printing forms for removing ink
from the indentations and sides, respectively, of the printing surfaces of
the applicable flexographic printing form, the ink-removing devices being
actuatable for removing the ink continuously or repeatedly at short
intervals during a printing job.
In accordance with another feature of the invention, the printing press
includes a control system connected to the device for removing ink and
having an input for introducing the cleaning intervals.
In accordance with a further feature of the invention, the drying devices
include UV projectors.
In accordance with an additional feature of the invention, the printing
press includes a wet offset printing press rebuilt for the letterset
process, wherein a groove in the printing form cylinder for receiving the
flexographic printing form is enlarged to between 1 and 2 mm, and into
which, instead of the dampening units, one device for removing ink from
the indentations and sides, respectively, of the flexographic printing
form is built into each of the individual printing units.
In accordance with yet another feature of the invention, the device for
removing the ink is a washing device.
In accordance with yet a further feature of the invention, the device for
removing the ink is a roller with a soft, ink accepting surface installed
instead of a dampening fluid applicator roller.
In accordance with a concomitant feature of the invention, the printing
cylinders in each printing unit and the transfer cylinders between the
printing units have at least twice the diameter of the printing form and
transfer cylinders, respectively.
In this manner, it is possible to print on platelike plastic material, of
the type used for check cards, telephone cards, chip cards, and so forth,
quickly and inexpensively with a quality previously thought unattainable,
because the printing press required for performing the method can be
assembled by modifying printing units built in great numbers for wet
offset printing. All that needs to be done is to change the depth of the
recess in the plate cylinder from a typical value of 0.3 to 0.5 mm to a
value of 1 to 2 mm, so that instead of the wet offset plates the
flexographic printing plates, which are thicker, can be fastened thereon.
Instead of the dampening unit which is otherwise customarily present, a
device for removing ink from the indentations or sides of the printing
surfaces of the flexographic printing plate is then installed: either a
washing device, or a roller with a soft, ink-accepting surface provided
instead of a dampening fluid applicator roller which is otherwise present.
Finally, if UV-curable inks are used, suitable drying units, i.e., UV
projectors suitably dimensioned with respect to power, can be installed in
the printing unit.
By dispensing with dampening, stability in ongoing production printing is
rapidly attained, and spoilage upon startup is drastically reduced which,
for the relatively costly plastic materials makes for a substantial cost
savings and improvement in quality.
The inking unit, conversely, can either be kept with a short inking unit or
replaced with a screen roller which cooperates with a chamber doctor
blade.
Depending upon the particular printing requirement, it may be expedient for
the flexographic printing form to be cleaned repeatedly at relatively
shorter or longer intervals during an ongoing printing job, or even before
each re-inking operation, so as to assure always replicable conditions for
every impression. It is therefore advantageous to provide a suitable
control system for that purpose, into which the cleaning intervals can be
input. In this way, the time needed to perform a printing job can be
suitably optimized for the printing quality desired.
Especially whenever the ink residues are to be removed before each
re-inking of the printing form, it is expedient to accomplish this with a
soft roller which rests in continuous contact on the flexographic printing
form and removes excess ink residues from the printing form, and then,
after subsequent distribution by a second roller, re-applies the ink in a
thin, even film.
Other features which are considered as characteristic for the invention are
set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a
method for multicolor printing of nonabsorbent material, and a printing
press for printing in accordance with the method, it is nevertheless not
intended to be limited to the details shown, since various modifications
and structural changes may be made therein without departing from the
spirit of the invention and within the scope and range of equivalents of
the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be best
understood from the following description of specific embodiments when
read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a greatly simplified diagrammatic side elevational view of a
printing press suitable for performing the method of the invention;
FIG. 2 is an enlarged fragmentary diagrammatic view of FIG. 1 showing one
printing unit of the printing press of FIG. 1 in a somewhat modified
version;
FIG. 3 is an enlarged fragmentary diagrammatic view of FIG. 2 showing a
device for cleaning the flexographic printing form in accordance with the
invention;
FIGS. 4 and 5 are further enlarged fragmentary diagrammatic views of FIG. 3
showing the encircled contact locations IV and V, respectively, between
the rollers 20 and 21, on the one hand, and between the roller 20 and the
flexographic printing form.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings and, first, particularly to FIG. 1 thereof,
there is shown therein a platelike plastic material 1 to be printed. It is
formed of a polyethylene plate 0.8 mm thick and 31 cm.times.61 cm in size,
from which, after the printing operation, thirty telephone cards will
later be stamped out. In the same hereinafter described manner, however,
it is also possible to print on printing stock of other material, such as
polypropylene, polyamides, polyester, Hostaphan films or foils, aluminum
vapor-deposited printing materials, and so forth.
The plates 1 are stacked in a feeder 2 and from there are delivered in a
conventional manner to the first of what in the case at hand are four
printing units, in line with one another and in unit construction. The
four printing units 3, 13, 23 and 33 are all of identical construction and
differ from one another only in the color that they print. Each printing
unit has a printing form cylinder 5 over which an aluminum-lined 1.16 mm
thick flexographic printing form 12 (note FIG. 5) is fastened. Such
flexographic printing forms are sold under the trade name Nyloflex FAE-L
by BASF, Ludwigshafen, Germany, for example. Because the printing unit 3
is a modified wet offset printing unit, and thus typically offset printing
plates 0.3 mm thick are fastened to the plate cylinder 5 thereof, the
recess in the cylinder 5 has been enlarged to suit the difference in
thickness, and taking into account any underlays which may be used.
To the printing form cylinder or plate cylinder 5, there is assigned a
previously existing inking unit 6, which is also suitable for the printing
of wet offset inks. Such an inking unit is described, for example, in U.S.
Pat. No. 5,388,514, and permits two modes of operation, either as a long
inking unit or as a short inking unit, depending upon the type of printing
job desired. For the coverings of the inking rollers, in any case, a
quality is selected which permits printing with UV inks. These rollers are
therefore mainly coated with polyurethane. A soft polyurethane coating
having a thickness of 6 to 10 mm is suitable, and the polyurethane has a
Shore A hardness of approximately 35.
Printing is performed cationically with UV flexographic printing inks, such
as those in the Bargoflex 36-0 series of inks, or radically with 39-2
inks. Such inks are sold, for example, by SICPA-Arberg A.G., in Arberg,
Switzerland. These inks have a viscosity of between 20 and 30 dP for the
colored inks and, with respect to their flowability, are near the familiar
range of present-day flexographic printing inks. Their somewhat higher
viscosity and higher tackiness, compared to inks which contain solvents
and/or water, assure an even, thin application of ink and a substantially
lesser increase in tonal value. It is thus possible to use even very
high-resolution printing blocks or plates, and the printing quality is
assured to remain constant over the production time. The inks contain
epoxy resins and are cured by UV radiation.
The printing unit 3 also has a transfer or rubber blanket cylinder 7, which
takes the printed image from the flexographic printing form. Associated
with the transfer cylinder 7 is a counterpressure or impression cylinder 8
having twice the diameter of the transfer or blanket cylinder 7, which
ensures that the stiff plates 1 will not deform excessively as they pass
through the printing press. The same effect is attained by a triple-size
transfer cylinder 9, from which the printed plates 1 are transferred to
the next printing unit 13.
Immediately after the printing in one of the four printing units 3, 13, 23,
33, the printed-on ink is cured by UV drying units 11 built into the
printing units. The drying units 11 are UV mercury medium-pressure
projectors with an output of approximately 150 watts per linear
centimeter. The UV projectors 11 contain quartz-coated aluminum
reflectors, which reflect the total UV component of the spectrum required
for the curing, but eliminate the infrared component in the manner of
cold-light mirrors, and thus assure a high UV radiation density with
minimal heat stress on the printing material.
Instead of the dampening unit otherwise located in the printing unit, a
washing device 10 is mounted on the plate cylinder 5. This washing device
10 is connected to a control system 34, to which the washing intervals, at
which the flexographic printing form fastened to the plate cylinder 5 is
repeatedly cleaned during an ongoing printing job, can be input via an
input unit 35, so as to prevent the ink from building up on the
flexographic printing form and in the indentations and on the sides
between the raised, printing locations on the flexographic printing form,
respectively.
When the plastic plates 1 are printed, they are accordingly printed in
succession in the four printing units 3, 13, 23 and 33 in the colors
black, cyan, magenta and yellow by indirect flexographic printing, i.e.,
by the letterset method, and the inks, respectively, are dried immediately
after each printing stage. At the same time, at short intervals, such as
every 4000 revolutions of the plate cylinder 5, the washing device 10 is
activated and the flexographic printing form is cleaned of excess ink.
The fully printed and dry plates are then stacked as usual in the delivery
4 of the printing press.
The printing unit 3 shown on a larger scale in FIGS. 2 to 5 is modified
somewhat over that of FIG. 1. Otherwise, however, those parts which remain
the same are provided with like reference numerals and therefore need not
be described again at this juncture.
As is readily apparent from the enlarged view of FIG. 2, the printing unit
13 additionally includes a washing device 17, with the aid of which the
rubber blanket fastened to the transfer or blanket cylinder 7 and the
counterpressure or impression cylinder 8 can both be cleaned.
Instead of the conventional inking unit 6 (FIG. 1) optimized for wet offset
printing, a screen roller 16 with a chamber doctor blade 26 is used to ink
the flexographic printing form 12 (FIG. 5). Such inking units based upon a
screen roller and chamber doctor blade are known per se and are therefore
believed to require no further description.
Instead of a dampening unit, a roller 20 with a soft surface of synthetic
rubber or polyurethane and a driven distributor roller 21 which rests
thereon and laterally oscillated and which has a hard, ink-accepting
surface are installed at the location whereat the dampening-fluid
applicator roller and the distributor roller for the dampening agent are
normally located. The rollers 20 and 21 revolve continuously; the roller
20 takes excess ink residues 12a (FIG. 5) which, during the printing
process, form on the sides of the printing surfaces of the flexographic
printing form, out of the indentations on the flexographic printing form
12 and then, after being distributed by the roller 21 (FIG. 4) re-applies
them in a thin ink film (12b) onto the printing locations on the
flexographic printing form 12 (FIG. 5). A doctor blade 22 can also be
positioned against the roller 21 with the aid of an actuator 32 (FIG. 2),
which is connected to the control system 34. In this manner, the raised
locations of the flexographic printing forms, and the rollers 20 and 21
can be cleaned, the ink being taken from the synthetic-rubber or
polyurethane-coated roller 20 and transferred to the roller 21, from the
surface of which the doctor blade 22 then removes it.
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